Hydroxyalkanoic acid and hydroxyalkanoice acid oligomer esters of retinol

ABSTRACT

Retinyl hydroxyesters and retinyl oligo-hydroxyesters were prepared using a chemoenzymatic process from retinol and short chain esters of hydroxycarboxylic acids or short chain esters of hydroxycarboxylic acids. The presence of the hydroxyl group on the acid can result in a mixture of esters from various oligomers of the hydroxycarboxylic acid. The retinyl ester products are readily enzymatically hydrolyzed in vitro, which indicates that application to the skin should result in release of the anti-aging ingredient retinol (without the inherent instability and irritation) along with the acid, which, if chosen appropriately, should also have desirable biological effects. This combination should be effective as an anti-aging skin care ingredient.

FIELD OF THE INVENTION

The present invention relates to retinyl esters and to processes forproducing them.

SUMMARY OF FIGURES

FIG. 1 shows the extent of enzymatic hydrolysis over time of retinyl3-hydroxybutyrate oligomers.

BACKGROUND OF THE INVENTION

Retinol (Vitamin A) and its derivatives have a long history as activeingredients in cosmetic compositions to improve the overall appearanceof the skin. Retinol itself is unstable and is irritating upon excessiveuse. Long-chain retinyl esters are therefore sometimes preferred becausethey are more stable and less irritating to the skin. These esters areexpected to be readily hydrolyzed in the skin to afford retinol formetabolism and thus efficacy. Depending on the fatty acid portion of theretinyl ester, the fatty acid hydrolysis product may provide additionalbenefits. Besides fatty acids, other structures, with various biologicalproperties, are also desired in retinyl conjugates, in order to improveand/or broaden the biological benefits.

Chemical preparation of retinyl esters involves either the reaction ofretinol with a long chain acid, acid chloride, or an ester, or by thetransesterification of a short-chain retinyl ester with a long-chainfatty acid ester. These processes use either harsh reagents or hightemperatures, which can cause degradation due to the instability of theretinol or the retinyl esters to these types of reaction conditions. Inaddition, these methods are generally incompatible with componentshaving reactive functionalities such as alcohols, unless the alcoholsare protected. The protection-deprotection adds cost, time, and waste tothe synthesis of these types of molecules.

There have been several reports of biocatalytic syntheses of retinylesters from retinol (O'Connor et. al. Aust. J. Chem. 1992, 45, 641;Maugard, et. al. J. Mol. Catal. B: Enzymatic 2000, 8, 275; Maugard et.al., Biotechnol. Prog. 2000, 16, 358; Maugard et. al. Biotechnol. Prog.2002, 18, 424.). These methods typically use long-chain acids thatfacilitate the ester formation and lack complicating reactive groups. Anexception is retinyl lactate, which has been prepared by enzymaticesterification of retinol with methyl lactate (Maugard, et. al. J. Mol.Catal. B: Enzymatic 2000, 8, 275; Maugard et. al., Biotechnol. Prog.2000, 16, 358; Maugard et. al. Biotechnol. Prog. 2002, 18, 424.). Thisis an unusual case, as the steric hindrance around the hydroxyl group ofthe lactate renders it relatively unreactive toward enzymaticesterification.

Retinyl esters tend to be more stable and more innocuous than retinolitself. The acid piece can be chosen for these purposes, or can beinfluenced by other biological considerations. For example,3-hydroxybutyric acid and esters thereof, including oligomers, arewell-known to be cellular energy sources, as noted by Stryer inBiochemistry, 4^(th) edition (1995), p 613, where he states that“Acetoacetate and J3-hydroxybutyrate are normal fuels of respiration andare quantitatively important as sources of energy.” A coupling ofβ-hydroxybutyrate or its oligomers with retinol, should it hydrolyze tothe constituent acid and alcohol in the cell, could have a doubleeffect—retinol would promote differentiation while the hydroxybutyratewould provide energy.

Thus retinyl esters of 3-hydroxybutyrate and 3-hydroxybutyrate oligomersas well as other hydroxyalkanoates would be novel materials that shouldbe of advantage in cosmetic anti-aging compositions.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to retinyl esters represented bythe general formula 1:

wherein R is selected from substituted and unsubstituted, branched- andstraight-chain, saturated, unsaturated, and polyunsaturated divalentC₁-C₂₂ alkyl, substituted and unsubstituted divalent C₃-C₈ cycloalkyl,substituted and unsubstituted divalent C₆-C₂₀ carbocyclic aryl, andsubstituted and unsubstituted divalent C₄-C₂₀ heterocyclic wherein theheteroatoms are selected from sulfur, nitrogen, and oxygen; R¹ isselected from hydrogen, substituted and unsubstituted, branched- andstraight-chain, saturated, unsaturated, and polyunsaturated C₁-C₂₂alkyl, substituted and unsubstituted C₃-C₈ cycloalkyl, substituted andunsubstituted C₆-C₂₀ carbocyclic aryl, and substituted and unsubstitutedC₄-C₂₀ heterocyclic wherein the heteroatoms are selected from sulfur,nitrogen, and oxygen; and n is 0-10; and mixtures of the foregoingesters.

In another aspect, R is selected from substituted and unsubstituted,branched- and straight-chain, saturated, unsaturated, andpolyunsaturated divalent C₁-C₁₈ alkyl, or a saturated or monounsaturatedstraight-chain C₁-C₁₀ alkyl; and R¹ is selected from hydrogen,substituted and unsubstituted, branched- and straight-chain, saturated,unsaturated, and polyunsaturated C₁-C₁₈ alkyl, and n is 0-10.

In another aspect, R is a substituted or unsubstituted, branched- orstraight-chain, saturated, unsaturated, or polyunsaturated divalentC₁-C₁₀ alkyl, or a saturated or monounsaturated straight-chain C₁-C₄alkyl; and R¹ is hydrogen, a substituted or unsubstituted, branched- orstraight-chain, saturated, unsaturated, or polyunsaturated C₁-C₁₈ alkyl,or C₁-C₁₂ alkyl, or C₁-C₄ alkyl; and n is 0-6, or mixtures thereof.

In yet another aspect, R is methyl, ethyl, or propyl; R¹ is methyl,ethyl, or propyl; and n is from 0 to 6, or mixtures thereof. In afurther aspect, R is methylene; R¹ is methyl, and n=1, 2, 3, and 4. Thatis, the retinyl esters may be a mixture of esters of varying lengths andincluding repeating units.

In another aspect, the retinyl esters may be derived from retinol andone or more hydroxy-substituted carboxylic acids, for example one ormore of 3-hydroxybutyric acid, 3-hydroxy-3-methylbutyric acid,3-hydroxyoctanoic acid, malic acid, 3-phenyl-3-hydroxypropanoic acid,10-hydroxydecanoic acid, 12-hydroxydodecanoic acid,16-hydroxyhexadecanoic acid, or ricinoleic acid.

In another aspect, the esters include oligomers comprised of more thanone repeating unit from the one or more hydroxy-substituted carboxylicacids.

In a further aspect, the invention relates to processes for producingthe retinyl esters just described, the processes comprising reactingretinol, in the presence of an enzyme, with an acid or short chain esterof a hydroxyalkanoate represented by formula 2

wherein R and R¹ are as already indicated, and R⁵ is chosen fromhydrogen or C₁-C₅ straight or branched chain alkane or alkene.

The processes may be carried out in a solvent chosen from diethyl ether,diisopropyl ether, tert-butyl methyl ether, tetrahydrofuran, benzene,toluene, xylene, hexane, heptane, cyclohexane, limonene,dichloromethane, dichloroethane, dibromoethane, tetrachloroethylene,chlorobenzene, acetonitrile, dimethyl formamide, or dimethyl sulfoxide,or mixtures thereof.

In another aspect, the process may be carried out in one or more oftoluene, limonene, a heptane, or acetonitrile. Alternatively, theprocess may be carried out in the absence of a solvent. Enzymes usefulaccording to the process of the invention include one or more of alipase, an esterase, or a protease, and especially a lipase.

In one aspect, the acid or short chain ester of a hydroxyalkanoaterepresented by formula 2 may comprise one or more of ethyl3-hydroxybutyrate or methyl 3-hydroxybutyrate.

In yet another aspect, the invention relates to cosmetic compositionsthat include the retinyl esters of the invention.

Further aspects of the invention are as disclosed and claimed herein.

DETAILED DESCRIPTION

As used herein, the terms “alkyl” and “alkyl groups” are intended toapply broadly to hydrocarbyl groups without regard to whether thecarbons are joined together with a single bond, a double bond, or even atriple bond, so long as the groups contain linked carbon atoms andhydrogen atoms, some of which hydrogen atoms may be substituted by otheratoms or groups of atoms, as is well-known in the art of organicchemistry.

Thus, in one aspect, the invention relates to retinyl esters representedby the general formula 1:

wherein R is selected from substituted and unsubstituted, branched- andstraight-chain, saturated, unsaturated, and polyunsaturated divalentC₁-C₂₂ alkyl, substituted and unsubstituted divalent C₃-C₈ cycloalkyl,substituted and unsubstituted divalent C₆-C₂₀ carbocyclic aryl, andsubstituted and unsubstituted divalent C₄-C₂₀ heterocyclic wherein theheteroatoms are selected from sulfur, nitrogen, and oxygen, and R¹ isselected from hydrogen, substituted and unsubstituted, branched- andstraight-chain, saturated, unsaturated, and polyunsaturated C₁-C₂₂alkyl, substituted and unsubstituted C₃-C₈ cycloalkyl, substituted andunsubstituted C₆-C₂₀ carbocyclic aryl, and substituted and unsubstitutedC₄-C₂₀ heterocyclic wherein the heteroatoms are selected from sulfur,nitrogen, and oxygen, and n is 0-10 or mixtures thereof.

The compounds of the invention may be racemic, enantiomericallyenriched, diasteroemerically enriched, substantially diastereomericallypure, or substantially enantiomerically pure.

In another aspect, the invention relates to species denoted bystructures 1 wherein R is selected from substituted and unsubstituted,branched- and straight-chain saturated divalent C₁-C₁₈ alkyl,substituted and unsubstituted, branched- and straight-chain divalentC₂-C₁₈ alkenyl, substituted and unsubstituted, branched- andstraight-chain divalent C₄-C₁₈ dienyl, substituted and unsubstituteddivalent C₃-C₈ cycloalkyl, substituted and unsubstituted divalent C₆-C₁₂carbocyclic aryl, substituted and unsubstituted divalent C₄-C₁₂heterocyclic, R¹ is selected from hydrogen, substituted andunsubstituted, branched- and straight-chain saturated C₁-C₁₈ alkyl,substituted and unsubstituted, branched- and straight-chain C₂-C₁₈alkenyl, substituted and unsubstituted, branched- and straight-chainC₄-C₁₈ dienyl, substituted and unsubstituted C₃-C₈ cycloalkyl,substituted and unsubstituted C₆-C₁₂ carbocyclic aryl, substituted andunsubstituted C₄-C₁₂ heterocyclic, n is 0-6, or mixtures thereof.

The saturated, unsaturated, and polyunsaturated alkyl and cycloalkylgroups which may be represented by R may be straight- or branched-chaindivalent hydrocarbon radicals containing up to about 22 carbon atoms andmay be substituted, for example, with one to five groups selected fromC₁-C₆-alkoxy, carboxyl, amino, C₁-C₁₅ aminocarbonyl, C₁-C₁₅ amido,cyano, C₂-C₆-alkoxycarbonyl, C₂-C₆-alkanoyloxy, hydroxy, aryl,heteroaryl, thiol, thioether, C₂-C₁₀ dialkylamino, C₃-C₁₅trialkylammonium and halogen. The terms “C₁-C₆-alkoxy”,“C₂-C₆-alkoxycarbonyl”, and “C₂-C₆-alkanoyloxy” are used to denoteradicals corresponding to the structures —OR², —CO₂R², and —OCOR²,respectively, wherein R² is C₁-C₆-alkyl or substituted C₁-C₆-alkyl. Theterms “C₁-C₁₅ aminocarbonyl” and “C₁-C₁₅ amido” are used to denoteradicals corresponding to the structures —NHCOR³, —CONHR³, respectively,wherein R³ is C₁-C₁₅-alkyl or substituted C₁-C₁₅-alkyl. The term“C₃-C₈-cycloalkyl” is used to denote a saturated, carbocyclichydrocarbon radical having three to eight carbon atoms. The term“halogen” is used to include fluorine, chlorine, bromine, and iodine.

The saturated, unsaturated, and polyunsaturated alkyl groups which maybe represented by R¹ may be straight- or branched-chain hydrocarbonradicals containing up to about 22 carbon atoms and may be substituted,for example, with one to five groups selected from C₁-C₆-alkoxy,carboxyl, amino, C₁-C₁₅ aminocarbonyl, C₁-C₁₅ amido, cyano,C₂-C₆-alkoxycarbonyl, C₂-C₆-alkanoyloxy, hydroxy, aryl, heteroaryl,thiol, thioether, C₂-C₁₀ dialkylamino, C₃-C₁₅ trialkylammonium andhalogen. The terms “C₁-C₆-alkoxy”, “C₂-C₆-alkoxycarbonyl”, and“C₂-C₆-alkanoyloxy” are used to denote radicals corresponding to thestructures —OR², —CO₂R², and —OCOR², respectively, wherein R² isC₁-C₆-alkyl or substituted C₁-C₆-alkyl. The terms “C₁-C₁₅ aminocarbonyl”and “C₁-C₁₅ amido” are used to denote radicals corresponding to thestructures —NHCOR³, —CONHR³, respectively, wherein R³ is C₁-C₁₅-alkyl orsubstituted C₁-C₁₅-alkyl. The term “C₃-C₈-cycloalkyl” is used to denotea saturated, carbocyclic hydrocarbon radical having three to eightcarbon atoms. The term “halogen” is used to include fluorine, chlorine,bromine, and iodine.

The branching and/or substitution of R and R¹ may connect to form aring.

The aryl groups which R may represent may include divalent phenyl,naphthyl, or anthracenyl and divalent phenyl, naphthyl, or anthracenylsubstituted with one to five substituents selected from C₁-C₆-alkyl,substituted C₁-C₆-alkyl, C₆-C₁₀ aryl, substituted C₆-C₁₀ aryl,C₁-C₆-alkoxy, halogen, carboxy, cyano, C₁-C₆-alkanoyloxy,C₁-C₆-alkylthio, C₁-C₆-alkylsulfonyl, trifluoromethyl, hydroxy,C₂-C₆-alkoxycarbonyl, C₂-C₆-alkanoylamino and —OR⁴, —S—R⁴, —SO₂—R⁴,—NHSO₂R⁴ and —NHCO₂R⁴, wherein R⁴ is phenyl, naphthyl, or phenyl ornaphthyl substituted with one to three groups selected from C₁-C₆-alkyl,C₆-C₁₀ aryl, C₁-C₆-alkoxy and halogen. The term “halogen” is used toinclude fluorine, chlorine, bromine, and iodine.

The aryl groups which R¹ may represent (or any aryl substituents) mayinclude phenyl, naphthyl, or anthracenyl and phenyl, naphthyl, oranthracenyl substituted with one to five substituents selected fromC₁-C₆-alkyl, substituted C₁-C₆-alkyl, C₆-C₁₀ aryl, substituted C₆-C₁₀aryl, C₁-C₆-alkoxy, halogen, carboxy, cyano, C₁-C₆-alkanoyloxy,C₁-C₆-alkylthio, C₁-C₆-alkylsulfonyl, trifluoromethyl, hydroxy,C₂-C₆-alkoxycarbonyl, C₂-C₆-alkanoylamino and —OR⁴, —S—R⁴, —SO₂—R⁴,—NHSO₂R⁴ and —NHCO₂R⁴, wherein R⁴ is phenyl, naphthyl, or phenyl ornaphthyl substituted with one to three groups selected from C₁-C₆-alkyl,C₆-C₁₀ aryl, C₁-C₆-alkoxy and halogen. The term “halogen” is used toinclude fluorine, chlorine, bromine, and iodine.

The divalent heterocyclic groups which R may represent include 5- or6-membered ring containing one to three heteroatoms selected fromoxygen, sulfur and nitrogen. Examples of such heterocyclic groups arepyranyl, oxopyranyl, dihydropyranyl, oxodihydropyranyl,tetrahydropyranyl, thienyl, furyl, pyrrolyl, imidazolyl, pyrazolyl,thiazolyl, isothiazolyl, oxazolyl, isoxazolyl, triazolyl, thiadiazolyl,oxadiazolyl, tetrazolyl, pyridyl, pyrimidyl, benzoxazolyl,benzothiazolyl, benzimidazolyl, indolyl and the like. The heterocyclicradicals may be substituted, for example, with up to three groups suchas C₁-C₆-alkyl, C₁-C₆-alkoxy, substituted C₁-C₆-alkyl, halogen,C₁-C₆-alkylthio, aryl, arylthio, aryloxy, C₂-C₆-alkoxycarbonyl andC₂-C₆-alkanoylamino. The heterocyclic radicals also may be substitutedwith a fused ring system, e.g., a benzo or naphtho residue, which may beunsubstituted or substituted, for example, with up to three of thegroups set forth in the preceding sentence. The term “halogen” is usedto include fluorine, chlorine, bromine, and iodine.

The heterocyclic groups which R¹ may represent (or any heteroarylsubstituents) include 5- or 6-membered ring containing one to threeheteroatoms selected from oxygen, sulfur and nitrogen. Examples of suchheterocyclic groups are pyranyl, oxopyranyl, dihydropyranyl,oxodihydropyranyl, tetrahydropyranyl, thienyl, furyl, pyrrolyl,imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, oxazolyl, isoxazolyl,triazolyl, thiadiazolyl, oxadiazolyl, tetrazolyl, pyridyl, pyrimidyl,benzoxazolyl, benzothiazolyl, benzimidazolyl, indolyl and the like. Theheterocyclic radicals may be substituted, for example, with up to threegroups such as C₁-C₆-alkyl, C₁-C₆-alkoxy, substituted C₁-C₆-alkyl,halogen, C₁-C₆-alkylthio, aryl, arylthio, aryloxy, C₂-C₆-alkoxycarbonyland C₂-C₆-alkanoylamino. The heterocyclic radicals also may besubstituted with a fused ring system, e.g., a benzo or naphtho residue,which may be unsubstituted or substituted, for example, with up to threeof the groups set forth in the preceding sentence. The term “halogen” isused to include fluorine, chlorine, bromine, and iodine.

Examples of the compounds of the invention include those represented byformula 1 wherein R is methylene, R¹ is methyl and n is from 0 to 6, andmixtures thereof.

In another aspect, the invention relates to retinyl esters representedby the general formula 1:

wherein R is selected from substituted and unsubstituted, branched- andstraight-chain, saturated, unsaturated, and polyunsaturated divalentC₁-C₁₈ alkyl, or C₁-C₁₂ alkyl, or C₁-C₁₀ alkyl, or a saturated ormonounsaturated straight-chain C₁-C₁₀ alkyl, or C₁-C₄ alkyl; and R¹ isselected from hydrogen, substituted and unsubstituted, branched- andstraight-chain, saturated, unsaturated, and polyunsaturated C₁-C₁₈alkyl, or C₁-C₁₂ alkyl, or C₁-C₄ alkyl; and n is 0-10, or 1-6, or 1-4,or mixtures thereof.

In various additional aspects, examples of the compounds of theinvention thus include those represented by formula 1 wherein R ismethyl, ethyl, or propyl, R¹ is methyl, ethyl, or propyl, and n is from0 to 6, and mixtures thereof. We note that if differenthydroxyl-substituted acids are used in the processes according to theinvention, each of the R and R1 groups may exist independently of oneanother, but that if a single hydroxyl-substituted acid is used, each ofthe defined R and R1 groups will be the same, and the retinyl estersproduced may include oligomers having varying lengths, such that theretinyl esters are mixtures of compounds in which n=0, n=1, n=2, n=3,etc. However, when n is defined as 0-6, for example, we do not mean tothereby excludes mixtures which contain compounds in which n=7, n=8,etc., although they will typically be present in minor amounts, if atall.

Other examples of the retinyl esters of the invention thus includecompounds and mixtures represented by formula 1 wherein R is methylene,R¹ is methyl, and n is from 0 to 6, and mixtures thereof containingcompounds in which n=0, n=1, n=2, n=3, and n=4.

In another aspect of the invention, the retinyl esters correspond to thegeneral formula 1:

wherein R is selected from substituted and unsubstituted, branched- andstraight-chain, saturated, unsaturated, and polyunsaturated divalentC1-C₂₂ alkyl, or C₁-C₁₈ alkyl, or C₁-C₁₂ alkyl, or an unsaturated,monounsaturated, or polyunsaturated straight-chain C₂-C₂₂ alkyl, orC₄-C₁₈ alkyl; and R¹ is selected from hydrogen, substituted andunsubstituted, branched- and straight-chain, saturated, unsaturated, andpolyunsaturated C₁-C₁₈ alkyl, or C₁-C₁₂ alkyl, or C₁-C₄ alkyl; and n is0-10, or 1-6, or 1-4, or mixtures thereof. In this aspect, the retinylesters may be derived from retinol and one or more hydroxy-substitutedcarboxylic acids, for example 3-hydroxybutyric acid,3-hydroxy-3-methylbutyric acid, 3-hydroxyoctanoic acid, malic acid,3-hydroxy-3-methylglutaric acid, 3-phenyl-3-hydroxypropanoic acid,10-hydroxydecanoic acid, 12-hydroxydodecanoic acid,16-hydroxyhexadecanoic acid, or ricinoleic acid.

The retinyl esters produced from these hydroxyl-substituted acids mayinclude oligomers comprised of more than one repeating unit from thefatty acid, depending upon the reactivity of the hydroxyl-substitutedportion of the acid.

Another embodiment of our invention is a novel enzymatic process for thepreparation of retinyl ester compounds represented by the generalformula 1:

wherein,

R is selected from substituted and unsubstituted, branched- andstraight-chain, saturated, unsaturated, and polyunsaturated divalentC₁-C₂₂ alkyl, substituted and unsubstituted divalent C₃-C₈ cycloalkyl,substituted and unsubstituted divalent C₆-C₂₀ carbocyclic aryl, andsubstituted and unsubstituted divalent C₄-C₂₀ heterocyclic wherein theheteroatoms are selected from sulfur, nitrogen, and oxygen, and R¹ isselected from hydrogen, substituted and unsubstituted, branched- andstraight-chain, saturated, unsaturated, and polyunsaturated C₁-C₂₂alkyl, substituted and unsubstituted C₃-C₈ cycloalkyl, substituted andunsubstituted C₆-C₂₀ carbocyclic aryl, and substituted and unsubstitutedC₄-C₂₀ heterocyclic wherein the heteroatoms are selected from sulfur,nitrogen, and oxygen, the compounds represented by formula 1 may beracemic, enantiomerically enriched, diasteroemerically enriched,substantially diastereomerically pure, or substantially enantiomericallypure, and n is 0-10 or mixtures thereof by reaction of retinol with anacid or short chain ester of a hydroxyalkanoate represented by generalformula 2

wherein R and R¹ are as indicated above and R⁵ is chosen from hydrogenor C₁-C₅ straight or branched chain alkane or alkene in the presence ofa lipase, esterase, or protease.

The process is carried out without solvent or in an inert solvent chosenfrom cyclic or acyclic ether solvents such as diethyl ether, diisopropylether, tert-butyl methyl ether, or tetrahydrofuran, aromatichydrocarbons such as benzene, toluene, or xylene, aliphatic or alicyclicsaturated or unsaturated hydrocarbons such as hexane, heptane,cyclohexane, or limonene, halogenated hydrocarbons such asdichloromethane, dichloroethane, dibromoethane, tetrachloroethylene, orchlorobenzene, polar aprotic solvents such as acetonitrile, dimethylformamide, or dimethyl sulfoxide, or mixtures thereof.

The preferred solvents are no solvent, toluene, limonene, heptanes, andacetonitrile. The process may be carried out at a temperature betweenabout −100° C. and the boiling point of the solvent, preferably about0-60° C., most preferably 20-50° C. The amount of acid or short-chainester 2 may be between 0.85 and 20 equivalents based on retinol, and ispreferably between 1 and 10 equivalents, most preferably between 1 and 4equivalents.

The enzyme used in the process may be chosen from a variety ofhydrolytic enzymes, for example a protease, a lipase, or an esterase.Preferred enzymes include lipases. These lipases may be in the form ofwhole cells, isolated native enzymes, or immobilized on supports.

Examples of suitable lipases include, but are not limited to, Lipase PS(from Pseudomonas sp), Lipase PS-C (from Psuedomonas sp immobilized onceramic), Lipase PS-D (from Pseudomonas sp immobilized on diatomaceousearth), Lipoprime 50T, Lipozyme TL IM, or Novozym 435 (Candidaantarctica lipase B immobilized on acrylic resin). Removal of the wateror alcohol byproducts, if desired, can be done chemically via a water oralcohol absorbent (e.g., molecular sieves) or by physical removal of thewater or alcohol. This by-product removal is preferably done byevaporation, either by purging the reaction mixture with an inert gassuch as nitrogen, argon, or helium, or by performing the reaction atreduced pressures, or both, as these conditions can afford >95%conversion of retinol to 1. The preferred pressure for the reaction isbetween 1 torr and ambient pressure, more preferable between 50 torr andambient pressure. Any organic solvent that is included in this processmay or may not be removed along with the water or alcohol. Examples of 2include ethyl 3-hydroxybutyrate and methyl 3-hydroxybutyrate.

The product 1 of the process may be isolated using methods known tothose of skill in the art, e.g., by extraction, filtration, orcrystallization.

The retinyl esters according to the present invention can be used incompositions, such as cosmetic compositions, skin care compositions andthe like. The compositions can be useful, for example, for reducing skinroughness, fine lines, and wrinkles, improving photo-damaged skin,regenerating skin, reducing skin hyper-pigmentation, and reducingirritation and/or inflammatory reaction in skin.

Typical cosmetic and/or skin care compositions of the invention containat least 0.001% by weight of the carbonates according to the presentinvention. For example, the compositions can contain from about 0.001%to about 20.0% by weight or from about 0.01% to about 10.0% by weight ofthe retinyl ester according to the present invention. Lowerconcentrations may be employed for less pronounced conditions, andhigher concentrations may be employed with more acute conditions.Suggested ranges also depend upon any adjunct ingredients employed inthe compositions.

The cosmetic and skin care compositions of the invention may alsocontain other skin conditioning ingredients in addition to retinylesters. Such compositions may include, but are not limited to, skin careingredients such as retinol, retinyl fatty acid esters, tetronic acid,tetronic acid derivatives, hydroquinone, kojic acid, gallic acid,arbutin, α-hydroxy acids, ascorbic acid and fatty acid esters ofascorbic acid. Such other ingredients are known to those of skill in theart.

Typically, topical application to skin sites is accomplished inassociation with a carrier. Where employed, the carrier is desirablyinert in the sense of not bringing about a deactivation or oxidation ofactive or adjunct ingredient(s), and in the sense of not bringing aboutany significant adverse effect on the skin areas to which it is applied.For example, the compounds according to the present invention may beapplied in admixture with a dermatologically acceptable carrier orvehicle (e.g., as a lotion, cream, ointment, soap, stick, or the like)so as to facilitate topical application and, in some cases, provideadditional beneficial effects as might be brought about, e.g., bymoisturizing of the affected skin areas.

Suitable preparations include lotions containing oils and/or alcoholsand emollients such as olive oil, hydrocarbon oils and waxes, siliconeoils, other vegetable, animal or marine fats or oils, glyceridederivatives, fatty acids or fatty acid esters or alcohols or alcoholethers, lecithin, lanolin and derivatives, polyhydric alcohols oresters, wax esters, sterols, phospholipids and the like, and generallyalso emulsifiers (nonionic, cationic or anionic), although some of theemollients inherently possess emulsifying properties. These same generalingredients can be formulated into a cream rather than a lotion, or intogels, or into solid sticks by utilization of different proportions ofthe ingredients and/or by inclusion of thickening agents such as gums orother forms of hydrophilic colloids.

The novel processes provided by the present invention are furtherillustrated by the following examples.

EXAMPLES Example 1 Preparation of Retinyl 3-Hydroxybutyrate (1a)oligomers (n=0-4)

To a vial was added retinol in heptane (58% retinol; 25.9 g; 15.0 gretinol; 52.4 mmol), ethyl 3-hydroxybutyrate (20.76 g; 157 mmol; 3equiv), and Novozym 435 (1.5 g). The mixture was stirred at roomtemperature and purged with a stream of nitrogen through the mixture for48 h to afford 96.7% conversion of retinol to a mixture of retinyl3-hydroxybutyrate oligomers. The mixture was diluted with toluene (30mL), filtered and the solid was washed with toluene (30 mL). The toluenesolution was washed with 1:1 water:methanol (60 mL) and the aqueousdecant was back-extracted with heptanes (25 mL). The combined organiclayer was washed with 1:1 water:methanol (60 mL), dried with sodiumsulfate, and concentrated to afford 17.79 g of 1a (R═CH₂, R¹═CH₃) as athick yellow oil. HPLC analysis indicated 3.7% retinol and 95.5% 1aoligomers. The proportion by HPLC is 1a, n=0 (53.7%), 1a, n=1 (32.9%),1a, n=2 (7.1%), 1a, n=3 (1.4%), and 1a, n=4 (0.3%).

HPLC and HPLC-MS (4.6×150 mm Zorbax SB-C8 column [Agilent], 3.5μthickness, 80:20 methanol:water (containing 0.1% trifluoroacetic acid)for 20 min, detection at 325 nm): t_(R) 6.6 min (retinol); t_(R) 8.0 min(1a, n=0, M⁺=372); t_(R) 8.8 min (1a, n=1, M⁺=458); t_(R) 9.7 min (1a,n=2, M⁺=544); t_(R) 10.6 min (1a, n=3, M⁺=630); t_(R) 11.8 min (1a, n=4,M⁺=716).

Example 2 Preparation of Retinyl Ricinoleate (1b)

To a vial was added retinol in toluene (54% retinol; 1.852 g; 1.0 gretinol; 3.49 mmol), ricinoleic acid (80%; 1.250 g; 4.19 mmol; 1.2equiv), and Novozym 435 (1 g). The mixture was sealed and stirred atroom temperature for 21 h to afford 83% conversion of retinol to 1b.

HPLC (4.6×150 mm Zorbax SB-C8 column [Agilent], 3.5μ thickness, 90:10methanol:water (containing 0.1% trifluoroacetic acid) for 7 min,gradient to 95:5 methanol:water (containing 0.1% trifluoroacetic acid)over 1 min, hold for 12 min, gradient to 100% methanol over 1 min, holdat 100% methanol, detection at 325 nm): t_(R) 3.9 min (retinol); t_(R)14.2 min (1b).

Example 3 Enzymatic Hydrolysis of Retinyl 3-Hydroxybutyrate (1a)oligomers (n=0-4)

Retinyl 3-hydroxybutyrate oligomers (1a; 100 mg) was dissolved in 2 mLof toluene. pH 7 Buffer (2 mL) was added. Novozym 435 (100 mg) wasadded, and the mixture was stirred vigorously at ambient temperature.The top layer was sampled at 1, 24, and 48 h and analyzed by HPLC. Theresults are shown in FIG. 1, and indicate significant hydrolysis toretinol over 48 h. A control reaction without enzyme showed nohydrolysis after 48 h.

1. Retinyl esters represented by the general formula 1:

wherein, R is selected from substituted and unsubstituted, branched- andstraight-chain, saturated, unsaturated, and polyunsaturated divalentC₁-C₂₂ alkyl, substituted and unsubstituted divalent C₃-C₈ cycloalkyl,substituted and unsubstituted divalent C₆-C₂₀ carbocyclic aryl, andsubstituted and unsubstituted divalent C₄-C₂₀ heterocyclic wherein theheteroatoms are selected from sulfur, nitrogen, and oxygen; R¹ isselected from hydrogen, substituted and unsubstituted, branched- andstraight-chain, saturated, unsaturated, and polyunsaturated C₁-C₂₂alkyl, substituted and unsubstituted C₃-C₈ cycloalkyl, substituted andunsubstituted C₆-C₂₀ carbocyclic aryl, and substituted and unsubstitutedC₄-C₂₀ heterocyclic wherein the heteroatoms are selected from sulfur,nitrogen, and oxygen; and n is 0-10. or mixtures thereof.
 2. The retinylesters of claim 1, wherein R is selected from substituted andunsubstituted, branched- and straight-chain, saturated, unsaturated, andpolyunsaturated divalent C₁-C₁₈ alkyl, or a saturated or monounsaturatedstraight-chain C₁-C₁₀ alkyl; and R¹ is selected from hydrogen,substituted and unsubstituted, branched- and straight-chain, saturated,unsaturated, and polyunsaturated C₁-C₁₈ alkyl, and n is 0-10.
 3. Theretinyl esters of claim 1, wherein R is a substituted or unsubstituted,branched- or straight-chain, saturated, unsaturated, or polyunsaturateddivalent C₁-C₁₀ alkyl, or a saturated or monounsaturated straight-chainC₁-C₄ alkyl; and R¹ is hydrogen, a substituted or unsubstituted,branched- or straight-chain, saturated, unsaturated, or polyunsaturatedC₁-C₁₈ alkyl, or C₁-C₁₂ alkyl, or C₁-C₄ alkyl; and n is 0-6, or mixturesthereof.
 4. The retinyl esters of claim 1, wherein R is methylene,ethylene, or propylene; R¹ is methyl, ethyl, or propyl; and n is from 0to 6, or mixtures thereof.
 5. The retinyl esters of claim 1, wherein Ris methylene; R¹ is methyl, and n=0, 1, 2, 3, and
 4. 6. The retinylesters of claim 1, wherein the retinyl esters are derived from retinoland one or more hydroxy-substituted carboxylic acids.
 7. The retinylesters of claim 6, wherein the one or more hydroxy-substitutedcarboxylic acids comprise one or more of 3-hydroxybutyric acid,3-hydroxy-3-methylbutyric acid, 3-hydroxyoctanoic acid, malic acid,3-hydroxy-3-methylglutaric acid, 3-phenyl-3-hydroxypropanoic acid,10-hydroxydecanoic acid, 12-hydroxydodecanoic acid,16-hydroxyhexadecanoic acid, or ricinoleic acid.
 8. The retinyl estersof claim 6, wherein the esters include oligomers comprised of more thanone repeating unit from the one or more hydroxy-substituted carboxylicacids.
 9. A process for producing the retinyl esters of claim 1, theprocess comprising reacting retinol, in the presence of an enzyme, withan acid or short chain ester of a hydroxyalkanoate represented byformula 2

wherein R and R¹ are as indicated in claim 1, and R⁵ is chosen fromhydrogen or C₁-C₅ straight or branched chain alkane or alkene.
 10. Theprocess of claim 9, wherein the process is carried out in a solventchosen from diethyl ether, diisopropyl ether, tert-butyl methyl ether,tetrahydrofuran, benzene, toluene, xylene, hexane, heptane, cyclohexane,limonene, dichloromethane, dichloroethane, dibromoethane,tetrachloroethylene, chlorobenzene, acetonitrile, dimethyl formamide, ordimethyl sulfoxide, or mixtures thereof.
 11. The process of claim 9,wherein the process is carried out in one or more of toluene, limonene,heptane, or acetonitrile.
 12. The process of claim 9, wherein theprocess is carried out in the absence of a solvent.
 13. The process ofclaim 9, wherein the enzyme comprises one or more of a lipase, anesterase, or a protease.
 14. The process of claim 9, wherein the enzymeis a lipase.
 15. The process of claim 9, wherein the acid or short chainester of a hydroxyalkanoate represented by formula 2 comprises one ormore of ethyl 3-hydroxybutyrate, methyl 3-hydroxybutyrate, or ricinoleicacid.
 16. A cosmetic composition comprising the retinyl esters of claim1.